Speaker
Description
The CMS Inner Tracker (IT) pixel detector is a key component of the Phase-2 upgrade, designed to operate under the extreme radiation levels and occupancies expected at the High-Luminosity LHC. This talk will present validation studies of IT pixel modules, focusing on the optimisation of CROC tuning parameters and their impact on threshold uniformity, noise performance, and detector response. Thermal studies will be discussed, evaluating module behaviour under operating conditions. Quality control procedures for large-scale production, including electrical characterisation and grading, will also be addressed, together with results from irradiation campaigns, illustrating performance at HL-LHC–equivalent fluences.
Summary (500 words)
The CMS Inner Tracker (IT) pixel detector is a key component of the Phase-2 upgrade, designed to operate under the extreme conditions of the High-Luminosity LHC (HL-LHC), with instantaneous luminosities up to (7.5 \times 10^{34}\,\mathrm{cm^{-2}s^{-1}}) and radiation levels approaching (10^{16}\,\mathrm{n_{eq}/cm^2}). The detector employs highly granular silicon pixel modules with cell sizes of (25 \times 100\,\mu\mathrm{m}^2), read out by radiation-hard ASICs implemented in 65\,nm CMOS technology. A serial powering scheme and high-speed data links are used to satisfy power and bandwidth requirements, while thermal stability is ensured through a two-phase CO(_2) cooling system operating below (-20^\circ\mathrm{C}). An overview of the IT design and layout, including the TBPX, TFPX, and TEPX subsystems, will be presented.
This contribution reports on studies of IT pixel modules performed in the context of ongoing large-scale production and qualification. The response of the modules is investigated as a function of CMS Read-Out Chip (CROC) configuration parameters. The dependence of threshold dispersion, noise, and hit efficiency on selected DAC settings is evaluated, and operating points ensuring stable and uniform detector response are identified. These studies are used to define tuning procedures applicable across production sites.
Thermal characterisation is carried out over a range of temperatures, including operating conditions below (-20^\circ\mathrm{C}). Variations in threshold, noise, leakage current, and operational stability are studied as a function of temperature, providing input to the definition of operating conditions and safety margins.
Quality control (QC) procedures implemented during module production are described. These include electrical functionality tests, threshold tuning, and bump-bond integrity checks using S-curve and crosstalk-based methods. Thermal cycling between (-35^\circ\mathrm{C}) and (+40^\circ\mathrm{C}) is performed to assess mechanical and electrical robustness. Automated test sequences and common validation protocols are used across multiple production centres to ensure consistent and reproducible results. Modules are graded based on noise, threshold uniformity, and the fraction of defective pixels.
Irradiation studies are performed to evaluate module behaviour after exposure to fluences representative of HL-LHC conditions. Measurements before and after irradiation are compared, focusing on the evolution of key parameters such as noise, threshold, and leakage current.
The current status of module production and qualification across the IT subsystems will be presented, in conjunction with results from read-out configuration studies, thermal measurements, quality control procedures, and irradiation campaigns. These results contribute to the definition of operating parameters and quality criteria for the CMS IT pixel detector.